Scandium has apparently never been recovered from zircon ore. While there are scandium ores, such ores are rare (as noted in U.S. Pat. No. 2,874,039, to Pruvot et al., which discloses a process for extraction of scandium from thorveitite ore). The separation of rare earths from ores by leaching (including with hydrochloric acid in one instance) is discussed in U.S. Pat. Nos. 2,722,471 (to Hirsch et al), 3,812,233 (to Duncan), and 2,735,747 (to Kasey). The separation of rare earths from thorium (including in acid leach liquors in one instance) is discussed in U.S. Pat. Nos. 2,990,244 (to Brown et al), 3,159,452, (to Lerner), and 3,087,148 (to Carter et al). The reduction of scandium chloride to metal is discussed in U.S. Pat. 2,941,867 (to Maurer).
Zircon ore is used for the production of zirconium metal. The converting of zircon ore (zircon sand) to zirconium metal generally utilizes the following operations: chlorination, separation (to remove hafnium), rechlorination (by processing similar to the initial chlorination), reduction, distillation (magnesium chloride and Mg vaporization for their removal from the zirconium), and double (or triple) arc melting to produce an ingot. The zirconium ingot can be then fabricated into various shapes.
With regard to chlorination, U.S. Pat. No. 4,244,935, issued to Dell on Jan. 13, 1981, relates a method of forming the chloride of a metal-oxygen containing substance based on a fluid coking technique. It should be noted that the commercial process for making zirconium metal utilizes a fluidized bed carbochlorination process at about 1000.degree. C. (temperature across the bed apparently varies up to 200.degree. C. or so), which produces a relatively impure, hafnium-containing zirconium tetrachloride and by-product silicon tetrachloride (which silicon tetrachloride by-product is relatively easily separated by differential condensation). U.S. Pat. No. 3,895,097, issued to Langenhoff et al. on July 15, 1975, also relates to a process for reacting metal oxides with chlorine.
The separation step is required as naturally occurring zirconium ores generally contain from 1 to 3 percent hafnium oxide relative to zirconium oxide. In order that the zirconium metal be acceptable as a nuclear reactor material, the hafnium content must first be reduced to low levels to minimize the effect of the high neutron absorption cross section of hafnium. This separation process is difficult due to the extreme chemical similarity of the two elements. A number of techniques have been explored to accomplish this separation, with the technique currently in use in the United States involving liquid-liquid extraction of aqueous zirconyl chloride thiocyanate complex solution using methyl isobutyl ketone, generally as described in U.S. Pat. No. 2,938,679, issued to Overholser on May 31, 1960, with the removal of iron impurities prior to solvent extraction as described in U.S. Pat. No. 3,006,719, issued to Miller on Oct. 31, 1961.
Commercially, reduction is by reacting gaseous zirconium tetrachloride with molten magnesium to produce zirconium metal (in relatively porous, so-called "sponge", form). Modifications to the reduction process have been suggested in many U.S. Pat. Nos. , including 4,440,384; 4,511,399; 4,556,420; 4,613,366; 4,637,831 and assigned to the same assignee.
With regard to "distillation" to remove magnesium chloride and Mg (by their vaporization) from the zirconium sponge, such distillation is usually performed at about 1050-1100.degree. C. (note, however that Kwon et al. in U.S. Pat. No. 4,711,664 teach that iron content can be lowered by distilling at about 934.degree. C.).
Consumable electrode vacuum arc melting is generally used to produce a consolidated ingot from the porous distilled sponge (generally the distilled sponge is broken up and then pressed into disks, for example, which disks are then welded together to form the consumable electrode. An improved consumable electrode is described in Weber's U.S. Pat. No. 4,539,688.
Recovery of materials from waste streams, is, of course, desirable. For example, Naitou et al. in U.S. Pat. No. 4,650,652, issued Mar. 7, 1987, describe a process for recovering high purity rare earth oxides from a waste rare earth phosphor (the process utilizes dissolving waste rare earth phosphor in an excess amount of acid, adding oxalic acid to obtain precipitates of rare earth oxylates, washing precipitates and baking precipitates).